The invention relates to a fixing device for fixing a linearly displaceable machine part relative to a fixedly supported machine part. One of the parts is provided in the form of a guiding block and the other one in the form of a bar member. The bar member passes through the guiding block in a bar guiding means. The guiding block has a controllable setting device and clamping members. The clamping members have through-holes which receive the bar member. The clamping members, in the guiding block, are settable by the setting device between a first and second position. In a first position, the clamping members clamp the bar member and in a second position, the clamping members, with play, release the bar member.
It is appreciated that, depending on the application, either the guiding block or the bar member can constitute the fixedly supported machine part. For example, if the fixing device is used in connection with pneumatic setting cylinders, the guiding block is firmly attached to the cylinder housing and constitutes the fixedly supported part. The bar member is formed directly by the piston rod of the setting cylinder. On the other hand, in linear guiding means of machine tools, it is the guiding bars which, as a rule, are fixedly arranged in a machine frame. The guiding block is connected to a carriage and thus constitutes the linearly driven part.
In the above applications, the fixing devices of the species do not comprise the bar member itself, but are only designed and prepared to receive a suitable bar member. They fulfill their function after the respective bar member has been added.
A fixing device is known from EP 0452 702 B1. A carriage, displaceable on guiding bars, and drivable by a piston rod can be fixed on the guiding bars. For this purpose, the device has two clamping members which are received in a cylindrical housing. The clamping members are provided in pairs and are symmetric relative to one another. In the region of their through-holes for the bar member, the clamping members are adapted to the cylindrical housing. The clamping members form semi-cylinders which are bored through approximately perpendicularly relative to the central axis.
On their substantially planar surfaces facing one another, the semi-cylinders have a symmetric wedge assembly which is loaded by an expanding pin. The pin is movable radially relative to the longitudinal axis of the guiding bar. Thus; the semi-cylinders are pivotable in opposite directions relative to the guiding bar. The expanding pin is inserted transversely into a setting piston which is guided in the cylindrical housing. As a result of the pivot movement, the clamping edges arranged opposite one another at an angle at the through-holes of the clamping members, come to rest on the bar member. As a result of which the latter, in a self-reinforcing way, the bar is axially clamped in. The pivot movement, which has a clamping effect, takes place under the influence of a compression spring acting on the setting piston. To release the bar member, with the help of the clamping members, the setting piston is loaded with a positive pressure force which overcomes the force of the compression spring.
As a result of the semi-cylindrical form of the clamping members, the respective outer clamping edges resting against the clamping member have a very disadvantageous shape. Accordingly, the carriage must be adapted to the setting direction, which extends radially relative to the guiding axis. This requires a disadvantageous spacious housing. As a result of the type of setting, the number of clamping members is limited to two. Due to the type of support provided for the clamping members, different holding forces are generated depending on the direction of load application. Thus, in each direction of load application, only one of the two clamping members builds up its highest possible holding force.
GB 2 012 856 A1 discloses a device with the piston rod of a hydraulic or pneumatic cylinder of the cylinder housing fixed by a locking device. The latter comprises either one single clamping member with a through-hole for the piston rod or a pair of clamping members. Each has a through-hole for the piston rod. The clamping members are supported outside the through-holes on one side in the cylinder housing. Further, the clamping members, while being loaded by a spring force, are tilted around one point of the supporting means. If a pair of clamping members are present, they are tilted in opposite directions. The single clamping member of one of the clamping members, as a function of the load on the piston rod, has a tendency to self-jam at the edges of the through-hole. Thus, to release the clamping member, it is necessary to apply positive force. This may result in a delay in the release of the piston rod.
U.S. Pat. No. 2,806,723 describes a telescopic support of variable length. An inner pipe is fixed in a sleeve inserted into an outer pipe. For this purpose, annular discs, with through-holes for the inner pipe, are inserted into the sleeve. The annular discs are supported at one point of their outer edge in the sleeve. The annular discs, in the opposite direction, are loaded by a compression spring in the sense of a tilting movement. The annular discs may form either a single, jointly supported and loaded group or two groups supported and loaded in opposite directions. In this case, too, one of the groups can jam when the supporting means is subjected to a load. Thus, it is necessary to apply positive mechanical forces in order to set the annular discs perpendicular relative to the sleeve to release the inner pipe.